A Comprehensive Forwarding Strategy in DTNs: Theory and Practice

Delay tolerant networks (DTNs) are featured by unpredictable mobility patterns and easily interrupted connections. Forwarding strategy has always been the research focus in DTNs, in order to improve a delivery ratio. An enormous amount of research works pay attention to solving the following two problems: whether to forward and how to forward. Therefore, forwarding metrics and forwarding strategies both play important roles in DTNs. In this paper, we consider a generalized random-waypoint model with heterogeneous nodes; the node's speed is regarded as the forwarding metric, which includes both short-term and long-term speed. Subsequently, we propose a theoretical, multicopy delegation forwarding based on short-term and long-term speed in DTNs (DFSL-T), which first determines a comprehensive mapping from short-term speed and long-term speed to the actual forwarding metric. Then, according to the forwarding metric and delegation forwarding strategy, DFSL-T utilizes some efficient nodes with higher forwarding metrics to assist in delivering messages, in order to improve the delivery ratio while reducing the forwarding cost. However, DFSL-T assumes that each node could achieve the average speeds of the others, which is impractical. In order to overcome this problem, we further propose a practical strategy (DFSL-P) through exchanging and evaluating the average speeds of each other. Finally, we conduct simulations based on the synthetic mobility pattern and real trace. The results show that compared with other multicopy forwarding strategies, DFSL-T and DFSL-P achieve higher forwarding efficiency, which is the result of delivery ratio divided by forwarding cost.